The invention relates to a draw-out low-voltage molded case circuit breaker comprising a fixed part, notably a connecting base or frame provided with stationary draw-in contacts, and a movable part able to be moved between a drawn-in position and a drawn-out position of the fixed part and having movable draw-in contacts which cooperate in the drawn-in position with the stationary draw-in contacts, said movable part comprising said molded case and housed inside the molded case breaking contacts, an operating mechanism for opening and closing of the breaking contacts and a trip device which brings about opening of the breaking contacts when a fault occurs.
A draw-out circuit breaker mounted on a base or a frame can be extracted or replaced quickly without access being had to the live parts, and with the installation remaining in service. For safety reasons, it is forbidden to draw-out an on-load circuit breaker and safety measures, automatically causing tripping of the circuit breaker in the course of the draw-out operation, have already been proposed. Such a device comprises for example a pin protruding out from the rear panel of the molded case, and cooperating with the trip bar of the circuit breaker to prevent any closing of the circuit breaker and to cause it to open as soon as the pin is in the protruding position. When the circuit breaker is fitted on the base or frame, the pin is pushed in so as to release the trip bar enabling the circuit breaker to be closed. The assembly is arranged to bring about tripping of the circuit breaker before it is drawn-out, and to prevent reclosing of the circuit breaker until the latter has been drawn-in again. Any incorrect operation is thus prevented, and draw-in and draw-out of the circuit breaker can be performed in perfect safety. The shortcoming of the state-of-the-art device is that it prevents tests being carried out on the drawn-out circuit breaker. To close the circuit breaker when it is drawn-out, it is in fact indispensable to press the pin in and to lock it in this depressed position, with the risk of a circuit breaker being drawn-in whose pin is locked and whose contacts are closed.
The object of the present invention is to achieve a draw-out circuit breaker equipped with a pre-tripping device, preventing any incorrect operation and enabling tests to be carried out on the apparatus in the drawn-out position.